Hi Maxbar,
A FileTable is a specialized user table that has a pre-defined and fixed schema, in other words, FileTable structure cant be altered.
As you want to associate Product table with Document FileTable, you can create another table with your user-defined attributes and a foreign key reference to the FileTable column path_locator.
For more details, please review the following article and similar thread.
https://www.microsoftpressstore.com/articles/article.aspx?p=2225060&seqNum=2
https://social.msdn.microsoft.com/forums/sqlserver/en-US/7a966f9d-b6ce-471a-a3c2-7e2d0201f2ea/when-to-use-filetable-and-db-design-questions
Thanks,
Lydia Zhang